We have a GD Momentum 381-M. We are not full time RVers, so our space usage and requirements are different than yours. That stated, we travel with an F3-T and an F3-L in the 15' garage. I made wheel chocks and fabricated a super-floor tie-down to register, align, and tie down the two machines with only 2 straps on each bike. My caution would be, based on your weight statement, that it may be a challenge to attach the tie down straps. your f450 would have more than enough capacity to pull that sort of rig.
Many voices have stated handling, tires, shocks, stopping, etc. One thing to pay attention to is the steering and wheel alignment. It is known that the Spyder steering geometry has "bump steering" as a result of the steering and front suspension design. As the back gets loaded and compresses, and some of that load is also transferred to the front suspension, the normal toe-in will change from toe-in to neutral or toe-out. Neutral to Toe-out will make the handling very "twitchty": the machine will want to suddenly pull left or right depending on road surface, cross wind, etc. Proper toe-in can be accommodated in the wheel alignment process: first, find a competent tech, then they must understand the loaded ride height of the machine to factor in when the wheel alignment is performed. So stated, it would be best to make any suspension and tire changes first, then have the front end aligned.
Wayne
